auerbach: effects of chemicals 135 



mutation research, in addition to and often instead of supplying the 

 chemist with food for speculation, is one of the best tools for ana- 

 lyzing the fascinating series of events that culminate in induced 

 mutation. The practical value of mutagen specificity depends on 

 economical considerations and not on theories about the origin of 

 specificity. If a treatment can be found that profitably produces 

 a desired type of mutation, this will be a tremendous practical 

 success, whatever its theoretical basis. Indeed, it seems to me that 

 specificity of the reaction between mutagen and DNA is least 

 likely to lead to such a success. Research with micro-organisms 

 strongly suggests that this type of specificity differs between alleles 

 and sites of the same locus; in general, it will therefore not appear 

 as locus specificity. The aim of mutation breeding, on the other 

 hand, is phenotypical specificity, that is the specific production of 

 mutations that yield a desired phenotypical effect. If such specificity 

 exists at all, it is more likely to occur at a late step in mutagenesis, 

 when mutations leading to similar final effects may have a common 

 biochemical pathway. A judicious combination of mutagenic and 

 anti-mutagenic treatment may be one approach to its detection. 



If we now look back at the questions with which Ave started 

 this stocktaking of progress in chemical mutagenesis, it turns out, 

 surprisingly, that the greatest progress has been made along the path 

 that at first seemed by far the steepest, the path directed towards the 

 detection of mutagen specificity. Progress along the two other paths, 

 directed towards analysis of the chemical nature of the gene and of 

 the relationship between intergenic and intragenic changes, has been 

 somewhat disappointing. I believe this has been due mainly to two 

 opposing tendencies on the part of investigators. One is the tendency 

 to disperse efforts by hunting for more and more mutagens. The 

 other, which comes into play when a new mutagen has been detected, 

 is the tendency to channel all efforts at analysis into the field of 

 nucleic acid chemistry. Outside these two methods of approach lie 

 many neglected possibilities of biological analysis, whose exploration 

 almost certainly will contribute to our understanding of the structure 

 of higher chromosomes and of the complexities of the mutagenic 

 processes. 



